Qualificatio theologica, or A condemnation writ in Blood

"And so it was, then, that by a unanimous and most just vote they condemned, deposed and anathematized him for being a violator and adulterer and for being responsible for the harshest of persecutions and countless offenses against the churches of God.  And their decision was in agreement with the vote of condemnation which had originally been made against him with great accuracy and canonical, i.e. conciliar, judgment by Nicholaus the pope.  Moreover, when they put their signatures on the decree of deposition, they did not merely sign in ink, but—horror of horrors (and I have heard this confirmed by those who do know)—they actually dipped the pen in the very blood of the Savior [(Ὑπογράφουσι δὲ τῇ καθαιρέσι, οὐ ψιλῷ τῷ μέλανι τὰ χειρόγραφα ποιούμενοι, ἀλλά (τὸ φρικωδέστατον), ὡς τῶν ειδότων ἀκήκοα διαβεβαιουμένων, καὶ ἐν αὐτῷ τοῦ Σωτῆρος τῷ αἵματι βάπτοντες τὸν κάλαμον)].  This was the way in which they excommunicated and condemned Photius and all those who had been ordained by him."

     Nicetas David:  The Life of Patriarch Ignatius:  text and translation by Andrew Smithies, with notes by John M. Duffy, Dumbarton Oaks texts 13, Corpus fontium historiae Byzantinae 51 (Washington, DC:  Dumbarton Oaks Research Library and Collection, 2013), chap. 63, pp. 88-91.
     Now that's what I would call a "theological note"!
     I was put onto this by Robert F. Taft, "'Communion' from the tabernacle—a liturgico-theological oxymoron," Worship 88, no 1 (January 2014):  9 (2-22), citing "Nicetas David Paphlagon (late ninth to early tenth century), Vita Ignatii archiepiscopi Constantinopolitani, Mansi[, Sacrorum conciliorum nova et amplissima collectio] 16:264-65 = PG 105:545CD."  Running a search on the Greek (above), I see that PG 105:488-574 has also been keyed in here.
     Taft cites two historians who "view the story with skepticism" (J. A. G. Hergenröther, Photius, Patriarch von Konstantinopel, 3 vols. (Regensburg:  Georg Joseph Manz, 1867-1869), 2:109 ff.; and F. Dvornik, The Photian schism:  history and legend (Cambridge:  Cambridge University Press, 1948), 149n4), but concludes that, though possibly apocryphal, "it would not have been invented had it been considered unthinkable at the time."
     Dvornik, who "comments on the 'tallness' of this anecdote" (Smithies-Duffy, 154n159), does little more than cite (the in his opinion usually over-credulous) Hergenröther, who says (I do not reproduce all of Hergenröther's footnotes):

Although many examples could in this way [(hiefür = hierdurch)] be also now cited (for example Baronius on the condemnation of the Monothelite Pyrrhus [(references to this and further examples in the footnote)]), nevertheless Nicetas does not appear to have been by his sources well-informed, since neither the Greek nor the Latin Acts contain any trace of this [event]; all other witnesses know nothing of it; and there is, in the whole course of the proceedings, no suitable place into which such an event [(Faktum)] could be inserted.  In the seventh session as well as in the two following no official documents were signed; only at the conclusion of the tenth session did those present, the emperor along with the prelates, sign [anything], and those signatures were meant to endorse [(bezogen sich auf)] the entire proceedings.  It is not improbable that, in accordance with similar events in Byzantium, for example what [(nach dem, was)] Photius himself is supposed to have done [(gethan haben soll)] in 866 [(vol. 1, p. 585, where 
Hergenröther's comment is that 'Wir würden gerne diese Angabe verwerfen und einen solchen Mißbrauch des Heiligsgten für unblaublich halten'!)], such a rumor developed and was believed by many, from whom Nicetas, too, heard the [story].  [But] the statement appears at least dubitable.

Obschon nun auch hiefür manche Beispiele angeführt werden können, wie denn Baronius die Verdammung des Monotheliten Pyrrhus anführt, so scheint doch Niketas von seinen Gewährsmännern nicht gut unterrichtet worden zu sein, da weder die griechischen noch die lateinischen Akten davon eine Spur enthalten, alle anderen Zeugen davon nichts wissen und im ganzen Verlauf der Verhandlungen sich keine passende Stelle findet, an die ein solches Faktum zu setzen wäre.  In der siebenten Sitzung sowie in den zwei folgenden wurden keine Aktenstücke unterschrieben; erst am Schluße der zehnten Sitzung unterzeichneten die Anwesenden, der Kaiser mitten unter den Prälaten, und diese Unterschriften bezogen sich auf die sämtlichen Verhandlungen.  Es ist nicht unwahrscheinlich, daß nach ähnlichen Vorkommnissen in Byzanz, nach dem, was Photius 866 selbst gethan haben soll, ein solches Gerücht sich bildete und Viele daran glaubten, woher es auch Niketas erfuhr; mindestens erscheint die Angabe als zweifelhaft.